Your reaction to a humorous situation might be partly determined by your DNA. Are you one to smile or laugh immediately at jokes, or do you just acknowledge them without expressing it in laughter? A new study focusing on emotional reactivity explained that your choice might be based on the make-up of your DNA. The findings are published in the American Psychological Association journal Emotion.

Short alleles of gene 5-HTTLPR

The study co-authored by Claudia M. Haase from Northwestern University and Ursula Beermann from the University of Geneva focused on the two versions of the gene 5-HTTLPR: its short and long alleles. The gene is involved in serotonin regulation, the neurotransmitter linked with depression and anxiety.

The specific gene variant – short alleles of the gene 5-HTTLPR – was linked with smiling and laughing more while watching funny videos. Those individuals with the longer version of the gene smiled and laughed less. Could this gene determine someone’s propensity to react by laughing or smiling?

The experiments: watching funny clips

The researchers carried out a series of experiments before reaching to that conclusion. In the first one, young adults were made to watch cartoons from “The Far Side” by Gary Larson and The New Yorker. In the second one, adults from different age groups watched a subtly humorous clip from the movie “Strangers in Paradise”. The last experiment was a discussion session whereby middle-aged and older spouses talked of a subject of disagreement in their marriage.

The reactions of the volunteers were captured in videos. The researchers then coded smiling and laughing via the “Facial Action Coding System”. The researchers wanted to distinguish between genuine smiling and laughter as opposed to the tendency to only smile or laugh out of politeness, or to hide negative feelings.

“So when you measure smiling and laughing, you want to be able to distinguish real laughs and smiles from the ones that aren’t,” co-author Beermann said.

“The important clues lie in the muscle around the eyes that produce the so-called ‘crow’s feet,'” Beermann said. “Those can only be seen in real smiles and laughs,” she said.

The saliva samples of the participants were then collected for analysis of the 5-HTTLPR gene. That was how the researchers found out that people with the short alleles of the gene inclined to smiling and laughing more than those with the long alleles.

Gene linked with both positive & negative emotions

The very same gene was correlated with negative emotions in the past by other researchers; the short alleles were linked with depression, anxiety, and substance abuse in other studies. People with the short alleles seemed to have higher negative emotions than those individuals who inherited the long alleles, according to other findings.

On the other hand, the new study, suggests that it is also linked with positive emotions. This would imply that people with short alleles are also more sensitive to emotional events in life.

It appears that the short alleles constitute a double-edged sword, conferring onto the person the ability to soar in positive environments and the downside of being more exposed in negative ones; in short, these people would be more sensitive to their surroundings, good or bad.

“Having the short allele is not bad or risky,” said Haase, an assistant professor in the Human Development and Social Policy program at Northwestern’s School of Education and Social Policy. “Instead, the short allele amplifies emotional reactions to both good and bad environments.”

“Our study provides a more complete picture of the emotional life of people with the short allele,” Haase added. “People with short alleles may flourish in a positive environment and suffer in a negative one, while people with long alleles are less sensitive to environmental conditions.”

“This study provides a dollop of support for the idea that positive emotions are under the same tent as negative ones, when it comes to the short allele,” Levenson said. “It may be that across the whole palate of human emotions, these genes turn up the gain of the amplifier. It sheds new light on an important piece of the genetic puzzle.”

However, genetics is not everything; again, the question of nurture versus nature arises.

“The fundamental truth of genes is that they don’t have the final say,” said senior author Levenson, a leading researcher in human emotions and professor in the department of psychology at UC-Berkeley. “There’s always an interaction between nature and nurture that shapes outcomes, and this study is another example of that.”